Carbohydrate composition of porcine ceruloplasmin

Abstract

Porcine ceruloplasmin is shown to contain 12–13 moles of glucosamine, 8 moles of sialic acid ( N-acetylneuraminic acid), 12 moles of mannose, 8 moles of galactose and 4 moles of fucose. Tryptic digestion of the protein results in the formation of the four main glycopeptide components in a yield of 70–80%. Each glycopeptide is almost homogeneous, and contains glucosamine, sialic acid, mannose, galactose and fucose. The molar ratios of the sugars are identical for each glycopeptide and approx. 3:2:3:2:1. The molecular weights of the glycopeptides are estimated to be 3300–4800 by gel filtration and ultracentrifugal analysis. The values are approximately identical with the minimal molecular weights calculated from the molar ratios of the constituents assumed to be integral. This suggests that each glycopeptide contains 3 moles of glucosamine, 2 moles of sialic acid, 3 moles of mannose, 2 moles of galactose and 1 mole of fucose. The glycopeptides are formed in the amounts of 0.6–1.0 mole from 1 mole of the protein. Porcine ceruloplasmin, therefore, is assumed to contain four heterosaccharide chains of similar carbohydrates compositions. The different amino acid compositions of the glycopeptides indicate that the two subunits of porcine ceruloplasmin are not identical.